F. H. Stewart 45 
liver lie obviously in dilated blood capillaries, venules, and veins. In the latter 
situations they are surrounded on all sides by red blood corpuscles. 
Ransom and Foster in one experiment found larvae in blood taken with 
a syringe from the portal vein, in another experiment one larva in blood from 
the pulmonary artery. They state, however, that accidental access of larvae 
from other sources could not be entirely excluded. 
The following table shows the breadth of Ascaris , Agchylostoma and Filaria 
larvae, compared with the diameter of blood capillaries: 
Maximum breadth 
mm. 
1. Ascaris suilla recently hatched, alive in salt solution ... 0 013 
2. Ascaris suilla recently hatched, mounted in Canada balsam 0-0098 
3. Ascaris larva of fifth day, from lung of rat, in weak subli¬ 
mate solution ... ... ... ... ... ... 0025 
4. Ascaris larva of sixth day, from liver, in salt solution ... 0-034 
5. Agchylostoma duodenale mature larva, living (Looss) ... 0-017 
6. Filaria hankrofti larva from human blood, living (Manson) 0-008-0-011 
7. Human capillary normally full of blood (Schafer) ... ... 0-007-0-008 
Comparing 1, 6 and 7, it is clear that an Ascaris larva within the first 24-48 
hours could pass through a capillary with a moderate degree of dilatation, 
but that it would probably be delayed in the passage. Larvae of the fifth or 
sixth days would be much delayed, and might rupture the capillary. 
The early appearance of larvae in the lungs, and in small numbers in remote 
organs such as the spleen and kidney, could be explained, as suggested by 
Ransom and Foster, by their passage direct in the blood stream through the 
liver, heart, and lungs. It is also possible that some traverse the lacteals, 
cysterna chyli, thoracic duct, subclavian veins, heart, and pulmonary artery, 
and thus reach the lungs without passing through the liver. 
The marked degeneration and disintegration of the liver cells around the 
larvae would permit of slow abnormal dilatation of the capillaries by the older 
animals, and their passage onward into the hepatic venules and veins. Even 
if rupture of the capillaries occurs, the larvae regain the blood stream in the 
veins, as is seen in the sections referred to above. 
Taking into consideration therefore the great frequency of the larvae in 
the liver, and their demonstrable presence in the blood vessels of this organ, 
I consider that the route described by me (Stewart, 1917, p. 226) is that 
followed by the great majority of the larvae, although a small proportion may 
doubtless follow the lymph stream, or perforate the diaphragm as described 
by Yoshida. In the blood and lymph streams they are guided by thigmo- 
tropism. It is not so easy to define the stimulus which would guide them 
under Yoshida’s hypothesis, although we cannot believe that their movements 
are entirely anarchic. 
